Substrate processing apparatus having a gas heating tube

ABSTRACT

A substrate processing apparatus comprises a heating member, a reaction tube body provided in the heating member and having a first gas introducing section and a gas exhausting section, a substrate holder disposed in the reaction tube body for horizontally holding a substrate within the reaction tube body between the first gas introducing section and the gas exhausting section, a gas heating tube provided in the heating member along the reaction tube body, and having a second gas introducing section and a gas discharging section which is in communication with the first gas introducing section of the reaction tube body, the gas heating tube being arranged such that a gas flowing in the gas heating tube first flows form the first gas introducing section side toward the gas exhausting section side, and then returns to flow from the gas exhausting section side toward the first gas introducing section side.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a substrate processing apparatus, andmore particularly, to a substrate processing apparatus for subjecting asemiconductor wafer to a process such as a film formation in a singlesubstrate-processing manner or a small number of substrates-processingmanner at a time.

2. Description of the Related Art

Conventionally, a reaction tube used with a substrate processingapparatus of a type described above has the structure shown in FIG. 15which is a plan view of a conventional substrate processing apparatus.

The substrate processing apparatus 200 is provided with a heater 70 anda reaction tube 80 disposed therein. The reaction tube 80 is providedwith a reaction tube body 81, a reaction gas introducing tube 85 and areaction tube flange 83. A reaction gas introducing hole 82 is providedat a central portion of an upstream of the reaction tube body 81. Thereaction gas introducing tube 85 is provided in communication with aninterior of the reaction tube body 81 through the reaction gasintroducing hole 82. The reaction tube body 81 is provided at itsdownstream with the reaction tube flange 83. The reaction tube flange 83is provided with a wafer transfer hole 84. In a state where asemiconductor wafer 90 is held in the reaction tube body 81, heating iseffected by the heater 70 and a reaction gas is introduced from thereaction gas introducing hole 82 into the reaction tube body 81, and isexhausted from the wafer transfer hole 84 of the reaction tube flange83, thereby processing of the semiconductor wafer 90 such as achievefilm formation.

According to the conventional reaction tube 80, however, the reactiongas is introduced into the reaction tube 80 without being sufficientlyheated and therefore, a temperature of the reaction gas upstream of thesemiconductor wafer 90 is lowered, and there is a problem that athickness of a film formed on the semiconductor wafer 90 becomesnonuniform.

SUMMARY OF THE INVENTION

Therefore, a main object of the present invention is to provide asubstrate processing apparatus capable of conducting a uniform substrateprocessing such as obtaining an excellent thickness distribution of aformed film.

According to a first aspect of the present invention, there is provideda substrate processing apparatus, including:

a heater;

a reaction tube body provided in the heater means, and having a firstgas introducing section and a gas exhausting section separated at apredetermined distance from each other in a predetermined firstdirection;

a substrate holder disposed in the reaction tube body and being capableof holding a substrate within the reaction tube body between the firstgas introducing section and the gas exhausting section in a state wherea main face of the substrate is substantially parallel to a first planewhich includes the first direction and a second direction perpendicularto the first direction; and

a gas heating tube provided in the heater means along the reaction tubebody, and having a second gas introducing section and a gas dischargingsection which is in communication with the first gas introducing sectionof the reaction tube body, the gas heating tube having a structurewherein a gas flowing in the gas heating tube first flows from the sideof the first gas introducing section toward the side of the gasexhausting section and then, returns to flow from the gas exhaustingsection side toward the first gas introducing section side.

According to a second aspect of the present invention, there is provideda hot-wall type substrate processing apparatus, including:

a heater;

a reaction tube body provided in the heater, the reaction tube bodyincluding: a first gas introducing section and a gas exhausting sectionseparated at a predetermined distance from each other in a predeterminedfirst direction; a first side plate substantially perpendicular to thefirst direction and having the first gas introducing section; a ceilingplate and a bottom plate substantially parallel to a first planeincluding the first direction and a second direction substantiallyperpendicular to the first direction; and second and third side plateswhich is substantially parallel to the first direction and issubstantially perpendicular to the first plane;

a substrate holder disposed in the reaction tube body and being capableof holding a substrate within the reaction tube body between the firstgas introducing section and the gas exhausting section in a state wherea main face of the substrate is substantially parallel to the firstplane; and

a gas heating tube provided in the heater along one of or both of thesecond side plate and the third side plate, and having a second gasintroducing section and a gas discharging section which is incommunication with the gas introducing section of the reaction tubebody.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and further objects, features and advantages of the presentinvention will become more apparent from the following detaileddescription taken in conjunction with the accompanying drawings,wherein:

FIG. 1 is a plan view, partially broken away, for explaining a substrateprocessing apparatus according to first and second embodiments of thepresent invention;

FIG. 2 is a sectional view taken along the line X2--X2 in FIG. 1;

FIG. 3 is an enlarged view of a portion in FIG. 1 surrounded by thecircle A;

FIG. 4 is a sectional view taken along the line X4--X4 in FIG. 3;

FIG. 5 is a sectional view taken along the line X5--X5 in FIG. 3;

FIG. 6 is a perspective view for explaining a reaction tube used in thesubstrate processing apparatus of the first embodiment;

FIG. 7 is a perspective view for explaining the reaction tube used inthe substrate processing apparatus of the first embodiment;

FIG. 8 is an enlarged view of the portion in FIG. 1 surrounded by thecircle A for explaining a reaction tube used in a substrate processingapparatus according to the second embodiment;

FIG. 9 is a sectional view taken along the line X9--X9 in FIG. 8;

FIG. 10 is a sectional view taken along the line X10--X10 in FIG. 8;

FIG. 11 is a plan view for explaining a substrate processing apparatusaccording to a third embodiment, in which a semiconductor wafer ismounted on a wafer mounting plate;

FIG. 12 is a sectional view taken along the line X12--X12 in FIG. 11,showing a state before mounting the semiconductor wafer on the wafermounting plate;

FIG. 13 is a perspective view for explaining a reaction tube used in thesubstrate processing apparatus of the third embodiment;

FIG. 14 is a perspective view for explaining the reaction tube used inthe substrate processing apparatus of the third embodiment; and

FIG. 15 is a plan view for explaining a reaction tube used in aconventional substrate processing apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(First Embodiment)

Referring to FIGS. 1 to 7, there is shown a substrate processingapparatus 100 of a single substrate-processing type according to a firstembodiment of the present invention. The substrate processing apparatus100 is provided with a heater 70, a reaction tube 10 provided in theheater 70, and a thermal insulator 72. Each of the heater 70 and thereaction tube 10 are covered at their upper, lower, left and rightportions with the thermal insulator 72, and are formed into a so-calledhot-wall type structure. The reaction tube 10 is provided with areaction tube body 20, a gas heating tube 40 and a reaction tube flange26. A wafer mounting plate 120 is provided in the reaction tube body 20.The wafer mounting plate 120 is formed with a space 124 having adiameter larger than that of a Si-semiconductor wafer 90. Three wafersupporting claws 122 are projectingly provided in the space 124. Thereaction tube body 20 and the gas heating tube 40 are made of quartz.

The reaction tube body 20 is substantially formed into a rectangularparallelepiped shape, and includes a ceiling plate 21, a bottom plate 22and side plates 23, 24 and 25. The ceiling plate 21 and the bottom plate22 are parallel to each other, and the side plates 23 and 24 areparallel to each other. The side plate 25 is perpendicular to theceiling plate 21, the bottom plate 22 and side plates 23 and 24. Thewafer mounting plate 120 is disposed, in the reaction tube body 20,parallel to the ceiling plate 21 and the bottom plate 22. One sheet ofthe Si-semiconductor wafer 90 is supported by the wafer supporting claws122 of the wafer mounting plate 120 and is disposed in the space 124. Asurface of the Si-semiconductor wafer 90 and an upper face of the wafermounting plate 120 are within the same plane. The Si-semiconductor wafer90 is held in parallel to the ceiling plate 21 and the bottom plate 22.

The side plate 25 is provided, at a height substantially equal to thesemiconductor wafer 90, with a rectangular opening 28 which is parallelto a surface of the semiconductor wafer 90 and which is long in alateral direction. The opening 28 extends from the vicinity of a cornerportion 31 between the side plates 25 and 24 to the vicinity of a cornerportion 32 between the side plates 25 and 23. The reaction tube flange26 is provided at a downstream of the reaction tube body 20 at theopposite side of the side plate 25. The reaction tube flange 26 isprovided with a wafer transfer hole 27 which is rectangular in shape.The wafer transfer hole 27 has a size substantially equal to a phantomopening of the reaction tube body 20 obtained by cutting the reactiontube body 20 in a direction intersecting a direction of a gas flow at aright angle.

The gas heating tube 40 includes a lower gas heating tube 42 and anupper gas heating tube 43. The lower gas heating tube 42 includessubstantially straight tubes 45, 46 and 47. The upper gas heating tube43 includes substantially straight tubes 48, 49 and 50. The tubes 45 and50 are provided in parallel to a surface of the semiconductor wafer 90along the outer side of the side plate 25, the tubes 46 and 48 areprovided in parallel to the surface of the semiconductor wafer 90 alongthe outer side of the side plate 23, and the tubes 47 and 49 areprovided in parallel to the surface of the semiconductor wafer 90 alongthe outer side of the side plate 24.

One end of the tube 44 is in communication with a central portion of thetube 45, and the other end of the tube 44 is formed with a gas supplyhole 41. One end of the tube 45 is in communication with one end of thetube 46, the other end of the tube 46 is in communication with one endof the tube 48, and the other end of the tube 48 is in communicationwith one end of the tube 50. The other end of the tube 45 is incommunication with one end of the tube 47, the other end of the tube 47is in communication with one end of the tube 49, and the other end ofthe tube 49 is in communication with the other end of the tube 50.

The tube 50 is provide with a plurality of gas discharging holes 60forming a line parallel to a surface of the semiconductor wafer 90 at aheight substantially equal to the semiconductor wafer 90. These gasdischarging holes 60 are arranged from the vicinity of the cornerportion 31 between the side plates 25 and 24 to the vicinity of thecorner portion 32 between the side plates 25 and 23. The opening 28formed in the side plate 25 is designed such as to expose all of theplurality of gas discharging holes 60 provided in the tube 50, and thesegas discharging holes 60 are in communication with the opening 28 of theside plate 25.

All of the reaction tube body 20, the gas heating tube 40, the reactiontube flange 26, the wafer mounting plate 120, the semiconductor wafer90, the tube 44, the opening 28, the plurality of gas discharging holes60 and the wafer transfer hole 27 are formed symmetrically.

The gas heating tube 40 is welded to the reaction tube body 20.

In a state where a sheet of the semiconductor wafer 90 is held in thereaction tube body 20, a reaction gas is supplied from the gas supplyhole 41 while being heated by the heater 70 to conduct a process such asa film formation.

The reaction gas supplied from the gas supply hole 41 is supplied to thecentral portion of the tube 45 through the tube 44. Thereafter, thereaction gas diverges in left and right directions within the tube 45,and respectively flow into the lower tubes 46 and 47 which are formedsymmetrically. The reaction gas, after passing through the tubes 46 and47, returns to flow into the upper tubes 48 and 49, respectively, andflows therethrough into opposite ends of the tube 50. Thereafter, thereaction gas is introduced into the reaction tube body 20 through thegas discharging holes 60 provided in the tube 50 forming a linelaterally as well as through the opening 28 provided in the side plate25. The gas, after reaction, is exhausted through the wafer transferhole 27 of the flange 26.

In the present embodiment, the reaction gas is supplied into thereaction tube body 20 after passing through the gas heating tube 40which is heated by the heater 70. Therefore, the reaction gas ispreheated and introduced into the reaction tube body 20. As a result, anupstream portion of the semiconductor wafer 90 is restrained from beingcooled by the reaction gas, which enhances the uniformity ofdistribution of temperature over the entire surface of the semiconductorwafer 90, and also enhances the uniformity of a thickness of a film overthe entire surface thereof which is formed on a surface of thesemiconductor wafer 90, especially the uniformity of the thickness ofthe film in a direction of a flow of the reaction gas. Further,depending on a kind or type of the gas, it is possible to sufficientlydecompose the reaction gas within the gas heating tube 40, and as aresult, a quality of the film is enhanced.

Further, because the gas heating tube 40 is disposed along the sideplates 23, 24 and 25 of the reaction tube body 20, the substrateprocessing apparatus 100 can be made small in size.

All of the reaction tube body 20, the gas heating tube 40, the reactiontube flange 26, the wafer mounting plate 120, the semiconductor wafer90, the tube 44, the opening 28, and the plurality of gas dischargingholes 60 are formed symmetrically and therefore, it is possible to keepthe balance in temperature between left and right sides, and to equalizeflow speed of the reaction gas introduced into the reaction tube body 20from left and right sides. As a result, it is possible to enhance theuniformity of a thickness of a film over the entire surface which isformed on a surface of the semiconductor wafer 90, especially theuniformity of the thickness of the film in a lateral direction withrespect to a direction of a flow of the gas.

Further, the tube 50 is provided with the plurality of gas dischargingholes 60 forming a line in parallel to a surface of the semiconductorwafer 90, and the side plate 25 is provided the opening 28 such as toexpose the gas discharging holes 60. Therefore, the reaction gas isintroduced like a shower, and the reaction gas flow above the surface ofthe semiconductor wafer 90 becomes a laminar flow, which furtherenhances the uniformity of a thickness of the film. In contrast, in thereaction tube 80 of the conventional structure as is shown in FIG. 15,because only one gas introducing hole 82 is provided, the gas flow abovethe semiconductor wafer 90 does not become a laminar flow and thus, athickness of the film formed on the semiconductor wafer 90 is prone tobe nonuniform.

The plurality of gas discharging holes 60 are provided from the vicinityof the corner portion 31 between the side plates 25 and 24 to thevicinity of the corner portion 32 between the side plates 25 and 23.Therefore, turbulence zones of the reaction gas introduced into thereaction tube body 20 can be decreased and as a result, the gas flow canbe formed into a laminar flow, and a replacement efficiency of the gascan be enhanced.

Further, in such a hot-wall type substrate processing apparatus, becausethe entire reaction tube body 20 is kept at a predetermined temperature,even if the gas heating tube 40 is disposed along the side plates 23, 24and 25, it is possible to sufficiently preheat the reaction gas.Furthermore, because the gas heating tube 40 is disposed along the sideplates 23, 24 and 25, and the gas heating tube 40 does not face theceiling plate 21 and the bottom plate 22, the heater 70 which faces theceiling plate 21 and the bottom plate 22 of the reaction tube body 20 isnot blocked or interrupted by the gas heating tube 40, and as a result,the uniformity of the distribution of temperature over the entiresurface of the semiconductor wafer 90 is enhanced.

Also, by disposing the gas heating tube 40 along the side plates 23, 24and 25 of the reaction tube body 20 as described above, it is possibleto restrain the substrate processing apparatus 100 from increasing itsheight, and it is easy to uniform the distribution of temperature overthe entire surface of the semiconductor wafer 90. In contrast, if thegas heating tube 40 is disposed along the ceiling plate 21 or the bottomplate 22 of the reaction tube body 20, the height of the substrateprocessing apparatus 100 is increased by such an amount. In order toprocess a large number of semiconductor wafers 90 in a small floorspace, piling up a plurality of reaction tube bodies 20 in a verticaldirection seems to be an effective way. In such a case, however, if eachof the gas heating tubes 40 is disposed along the ceiling plate 21 orthe bottom plate 22 of the reaction tube body 20, the number of thereaction tube bodies 20 which can vertically be piled up is reduced andthus, the number of semiconductor wafers 90 per unit area is reduced.

If the gas heating tube 40 is disposed along the ceiling plate 21 or thebottom plate 22 of the reaction tube body 20, because the ceiling plate21 and the bottom plate 22 are provided in parallel to a major surfaceof the semiconductor wafer 90, it is difficult to make uniform thedistribution of temperature over the entire surface of the semiconductorwafer 90 unless the gas heating tube 40 is disposed uniformly along theceiling plate 21 or the bottom plate 22 of the reaction tube body 20.Further, such a structure itself in which the gas heating tube 40 isuniformly disposed along the ceiling plate 21 or the bottom plate 22 ofthe reaction tube body 20 is difficult, which increases manufacturingcosts. In contrast, if the gas heating tube 40 is disposed along theside plates 23, 24 and 25 of the reaction tube body 20, it is possibleto easily make uniform the distribution of temperature over the entiresurface of the semiconductor wafer 90 with a simple structure.

In the present embodiment, taking into consideration the fact that theamount of gas diverged into the left and right gas heating tube may notalways be equal to each other, the left and right portions of the gasheating tube are joined to each other at their end portions, so as tomoderate a difference in the amount of gas between the left and rightsides of the gas heating tube. Further, in order to avoid disturbing thedistribution of temperature in the vicinity of the semiconductor wafer90, the gas heating tube 40 is disposed at a location away from the bothsides of the semiconductor wafer.

(Second Embodiment)

In the first embodiment described above, the tube 50 of the gas heatingtube 40 is provided with the plurality of gas discharging holes 60, andthe side plate 25 of the reaction tube body 20 is provided with theopening 28 which exposes the plurality of gas discharging holes 60.However, as is shown in FIGS. 1, 2 and 8 to 10, the second embodimentdiffers from the first embodiment in that the side plate 25 of thereaction body 20 is provided with a plurality of gas introducing holes128 such as to form a line in parallel to the semiconductor wafer 90 ata height substantially equal to the semiconductor wafer 90, and the tube50 is provided with an opening 160 which is long in a lateral directionand which is in communication with the plurality of gas introducingholes 128. Other structures are the same as those of the firstembodiment.

Also, in the present embodiment, the reaction gas is supplied into thereaction tube body 20 after passing through the gas heating tube 40which is heated by the heater 70. Therefore, the reaction gas ispreheated and introduced into the reaction tube body 20. As a result, anupstream portion of the semiconductor wafer 90 is restrained from beingcooled by the reaction gas, which enhances the uniformity ofdistribution of temperature over the entire surface of the semiconductorwafer 90, and also enhances the uniformity of a thickness of a film overthe entire surface thereof which is formed on a surface of thesemiconductor wafer 90, especially the uniformity of the thickness ofthe film in a direction of a flow of the reaction gas. Further,depending on a kind or type of the gas, it is possible to sufficientlydecompose the reaction gas within the gas heating tube 40, and as aresult, a quality of the film is enhanced.

Further, because the gas heating tube 40 is disposed along the sideplates 23, 24 and 25 of the reaction tube body 20, the substrateprocessing apparatus 100 can be made small in size.

These gas introducing holes 128 are arranged from the vicinity of thecorner portion 31 between the side plates 24 and 25 to the vicinity ofthe corner portion 32 between the side plates 23 and 25. All of thereaction tube body 20, the gas heating tube 40, the reaction tube flange26, the wafer mounting plate 120, the semiconductor wafer 90, the tube44, the opening 160, the plurality of gas introducing holes 128 and thewafer transfer hole 27 are formed symmetrically.

Therefore, it is possible to keep the balance in temperature betweenleft and right sides, and to equalize flow speed of the reaction gasintroduced into the reaction tube body 20 from left and right sides. Asa result, it is possible to enhance the uniformity of a thickness of afilm over the entire surface which is formed on a surface of thesemiconductor wafer 90, especially the uniformity of the thickness ofthe film in a lateral direction with respect to a direction of a flow ofthe gas.

Further, the side plate 25 is provide with the plurality of gasintroducing holes 128 forming a line in parallel to a surface of thesemiconductor wafer 90, and the tube 50 is provided the opening 160 suchas to communicate with the plurality of gas introducing holes 128.Therefore, the reaction gas is introduced like a shower, and thereaction gas flow above the surface of the semiconductor wafer 90 becomea laminar flow, which further enhances the uniformity of a thickness ofthe film.

The plurality of gas introducing holes 128 are provided from thevicinity of the corner portion 31 between the side plates 25 and 24 tothe vicinity of the corner portion 32 between the side plates 25 and 23.Therefore, turbulence zones of the reaction gas introduced into thereaction tube body 20 can be decreased and as a result, the gas flow canbe formed into a laminar flow, and a replacement efficiency of the gascan be enhanced.

(Third Embodiment)

In the above described first embodiment, a tip end 401 of the hasheating tube 40 extends beyond the semiconductor wafer 90 and the wafermounting plate 120 and reaches the vicinity of the reaction tube flange26, and the gas heating tube 40 is provided along the side plates 23 and24 of the reaction tube body 20. However, as is shown in FIGS. 11 to 14,the third embodiment differs from the first embodiment in that the gasheating tube 40 is provided along the side plates 23 and 24 of thereaction tube body 20 such that the gas heating tube 40 is turned downor bent back before the center of the semiconductor wafer 90. Otherstructures are the same as those of the first embodiment.

The semiconductor wafer 90 is placed on a tweezer 130 and transferredinto the reaction tube body 20, and is placed on the wafer supportingclaws 122 of the wafer mounting plate 120 and disposed in a space 124.Further, the semiconductor wafer 90 on the wafer mounting plate 120 isplaced on the tweezer 130 and carried out from the reaction tube 10. Atthose times, in order to determine a position of the tweezer 130 whichtransfers the semiconductor wafer 90 and an operating range of thetweezer 130, a teaching process is conducted. When the teaching processis conducted, the thermal insulator 72 and the heater 70 are detached.Clearances in all horizontal directions of the semiconductor wafer 90and the wafer mounting plate 120 are checked by vertically seeing fromabove the reaction tube 10 through the ceiling plate 21. Clearances invertical direction is also checked by horizontal observation through theside plate 23 and/or the side plate 24. Points of such checking of theclearances in vertical direction are: to check a height of the wafermounting plate 120 so that the wafer mounting plate 120 and thesemiconductor wafer 90 do not interfere with each other when the tweezer130 on which the semiconductor wafer 90 is carried passes above thewafer mounting plate 120; and to check a vertical stroke motion of thetweezer 130 conducted when the semiconductor wafer 90 placed on thetweezer 130 is lowered to be placed on the wafer mounting plate 120, andthe semiconductor wafer 90 placed on the wafer mounting plate 120 ispicked up by the tweezer 130.

According to the third embodiment, when the reaction tube body 20 isviewed from the direction of the side plate 23 or 24, more than halfportion of the semiconductor wafer 90 can be observed, and the wafermounting plate 120 can also be observed from its one end 121 to a regionbeyond the central portion of the space 124 in which the semiconductorwafer 90 is to be provided. Therefore, when the teaching process isconducted, because the semiconductor wafer 90 and the wafer mountingplate 120 can sufficiently be observed, the teaching process can easilybe conducted.

For conducting the teaching process, when the reaction tube body 20 isviewed from the direction of the side plate 23 or 24, it is preferablethat at least a region from the one end 121 of the wafer mounting plate120 to one end 91 of the semiconductor wafer 90 can be observed.Further, when the reaction tube 10 is viewed from the direction of theside plate 23 or 24, it is more preferable that at least a half of thesemiconductor wafer 90, as well as a region of the wafer mounting plate120 from its one end 121 to at least the central portion of the space124 in which the semiconductor wafer 90 is to be provided. Therefore, itis preferable to provide the gas heating tube 40 along the side plates23 and 24 of the reaction tube body 20 such that the gas heating tube 40is bent back before the one end 91 of the semiconductor wafer 90, and itis more preferable to provide the gas heating tube 40 along the sideplates 23 and 24 of the reaction tube body 20 such that the gas heatingtube 40 is bent back before the center or the vicinity of the center ofthe semiconductor wafer 90.

In the third embodiment, a length of the gas heating tube 40 is shorterthan that of the first embodiment. However, a length from the centralportion 451 of the tube 45 through the tubes 46 and 48 to the cornerportion 52 is set 240 mm or longer, and a length from the centralportion 451 of the tube 45 through the tubes 47 and 49 to the cornerportion 51 is set 240 mm or longer. Therefore, the reaction gasintroduced from the gas discharging hole 60 provided in the vicinity ofthe corner portions 52 (32) and 51 (31) is sufficiently heated up to thesame temperature as that in the reaction tube body 20. Therefore,according to the third embodiment also, the reaction gas is sufficientlypreheated by the gas heating tube 40 and is introduced into the reactiontube body 20. As a result, an upstream portion of the semiconductorwafer 90 is restrained from being cooled by the reaction gas, whichenhances the uniformity of distribution of temperature over the entiresurface of the semiconductor wafer 90, and also enhances the uniformityof a thickness of a film over the entire surface which is formed on asurface of the semiconductor wafer 90, especially the uniformity of thethickness of the film in a direction of a flow of the reaction gas.Further, depending on a kind or type of the gas, it is possible tosufficiently decompose the reaction gas within the gas heating tube 40,and as a result, a quality of the film is enhanced.

Further, because the gas heating tube 40 is bent back, it is possible toshorten the length of that region of the gas heating tube 40 whichextends along the side plates 23 and 24 of the reaction tube body 20while keeping a sufficient length of a course of the reaction gasflowing through the gas heating tube 40. Therefore, it is possible tosufficiently preheat the reaction gas by the gas heating tube 40, and toincrease that region of the reaction tube body 20 which can be observedthrough the side plates 23 and 24 of the reaction tube body 20 withoutbeing interrupted by the gas heating tube 40.

Also, because the gas heating tube 40 is disposed along the side plates23 and 24, not along the ceiling plate 21 and the bottom plate 22, thesemiconductor wafer 90 can be observed over its entire range through theceiling plate 21 or the bottom plate 22, and the space 124 of the wafermounting plate 120 and the wafer supporting claws 122 can also beobserved over their entire ranges. Therefore, it is possible to easilyand reliably conduct the teaching process in all directions on ahorizontal plane for a process in which the semiconductor wafer 90 isplaced on or taken out from the wafer mounting plate 120. In this way,the teaching process in all horizontal directions can be conducted byobserving through the ceiling plate 23 or the bottom plate 22.Therefore, a teaching process through the side plate 23 or 24 can beconducted only for a vertical direction, and such teaching is possibleonly if a portion, rather than the entire, of the semiconductor wafer 90can be observed. At that time, if about half or more of thesemiconductor wafer 90, or about half or more of the space 124 of thewafer mounting plate 120 can be observed, the teaching process for aprocess in which the semiconductor wafer 90 is placed on or taken outfrom the wafer mounting plate 120 can be conducted easier and morereliably.

The gas heating tube 40 is disposed along the side plates 23, 24 and 25of the reaction tube body 20. The gas heating tube 40 is welded to thereaction tube body 20. The tube 50 is provide with a plurality of gasdischarging holes 60 forming a line parallel to a surface of thesemiconductor wafer 90. These gas discharging holes 60 are arranged fromthe vicinity of the corner portion 31 (51) between the side plates 25and 24 to the vicinity of the corner portion 32 (52) between the sideplates 25 and 23. These gas discharging holes 60 are in communicationwith the opening 28 formed in the side plate 25. All of the reactiontube body 20, the gas heating tube 40, the reaction tube flange 26, thewafer mounting plate 120, the semiconductor wafer 90, the tube 44, theopening 28, the plurality of gas discharging holes 60 and the wafertransfer hole 27 are formed symmetrically.

In the first and third embodiments, the tube 50 of the gas heating tube40 is provided with the plurality of gas discharging holes 60, and theside plate 25 of the reaction tube body 20 is provided with the opening28 which is in communication with these plurality of gas dischargingholes 60 and which exposes the gas discharging holes 60. In the secondembodiment, the tube 50 of the gas heating tube 40 is provided with theplurality of gas introducing holes 128, and the tube 50 of the gasheating tube 40 is provided with the opening 160 which is incommunication with these plurality of gas introducing holes 128.Alternatively, the tube 50 of the gas heating tube 40 may be providedwith a plurality of gas discharging holes forming a line in parallel toa surface of the semiconductor wafer 90 at a height substantially equalto the semiconductor wafer 90, and the side plate 25 of the reactiontube body 20 may also be provided with a plurality of gas introducingholes which respectively correspond to these gas discharging holes. Insuch a case also, all of the reaction tube body 20, the gas heating tube40, the reaction tube flange 26, the wafer mounting plate 120, thesemiconductor wafer 90, the tube 44, the plurality of gas dischargingholes, the plurality of gas introducing holes and the wafer transferhole 27 are formed symmetrically.

In the first to third embodiments, the substrate processing apparatus isof a single substrate-processing type in which a sheet of thesemiconductor wafer 90 is held in the reaction tube body 20. But itshould be noted that the present invention can preferably be applied toa substrate processing apparatus in which a small number of substrates,preferably, two sheets of the semiconductor wafers 90 are held in thereaction tube body 20.

What is claimed is:
 1. A substrate processing apparatus, comprising:aheater; a reaction tube body having a first gas introducing section anda gas exhausting section separated by a distance; a substrate holderdisposed in said reaction tube body and being capable of holding asubstrate within said reaction tube body between said first gasintroducing section and said gas exhausting section; a gas heating tubeprovided along said reaction tube body and not between said heater andsaid reaction tube body, and having a second gas introducing section anda gas discharging section which is in communication with said first gasintroducing section of said reaction tube body; and a thermal insulatorcovering said heater, said reaction tube body and said gas heating tube.2. A substrate processing apparatus as recited in claim 1 wherein saidgas heating tube has a structure such that a gas flowing in said gasheating tube flows from the side of said first gas introducing sectiontoward the side of said gas exhausting section, and then returns to flowfrom said gas exhausting section side toward said first gas introducingsection side.
 3. A substrate processing apparatus as recited in claim 1,whereinsaid first gas introducing section and said gas exhaustingsection are separated in a first direction, said reaction tube bodyincludes a first plate substantially perpendicular to said firstdirection, a second plate and a third plate substantially parallel to afirst plane which includes said first direction and a second directionperpendicular to said first direction, and fourth and fifth plates whichare substantially parallel to said first direction and are substantiallyperpendicular to said first plane, said first gas introducing sectionbeing provided in said first plate, said gas heating tube being disposedalong one or more of said first plate, said fourth plate and said fifthplate, said substrate holder is capable of holding a substrate withinsaid reaction tube body in a state where a face of said substrate to beprocessed is substantially parallel to said first plane, and said heaterfaces one or both of said second and third plates.
 4. A substrateprocessing apparatus as recited in claim 3, whereinsaid gas heating tubeis disposed along one or both of said fourth plate and said fifth plateand has a structure such that a gas flowing in said gas heating tubeflows from said first gas introducing section side toward said gasexhausting section side, and then returns to flow from said gasexhausting section side toward said first gas introducing section side.5. A substrate processing apparatus as recited in claim 3, wherein saidgas heating tube is disposed along said first, fourth and fifth plates.6. A substrate processing apparatus as recited in claim 5, wherein saidgas heating tube has a structure such that the gas flowing in said gasheating tube flows from said first gas introducing section side towardsaid gas exhausting section side respectively along said fourth andfifth plates, then returns to flow from said gas exhausting section sidetoward said first gas introducing section side respectively along saidfourth and fifth plates, and then flows along said first plate.
 7. Asubstrate processing apparatus as recited in claim 6, wherein said gasheating tube has a structure such that the gas flowing in said gasheating tube first flows, along said first plate, from substantially acentral portion of said first plate in said second direction toward saidfourth and fifth plates, then flows from said first gas introducingsection side toward said gas exhausting section side respectively alongsaid fourth and fifth plates, then returns to flow from said gasexhausting section side toward said first gas introducing sectionrespectively along said fourth and fifth plates, and then flows alongsaid first plate.
 8. A substrate processing apparatus as recited inclaim 3, whereinsaid gas heating tube includes first and second tubesdisposed in said first direction along said fourth plate, third andfourth tubes disposed in said first direction along said fifth plate, afifth tube disposed in said second direction along said first plate, anda gas introducing tube, said second gas introducing section includingsaid gas introducing tube, said gas introducing tube being incommunication with one end of each of said first and third tubes, theother end of said first tube being in communication with one end of saidsecond tube, the other end of said third tube being in communicationwith one end of said fourth tube, the other end of said second tubebeing in communication with one end of said fifth tube, the other end ofsaid fourth tube being in communication with the other end of said fifthtube, and said fifth tube including said gas discharging section whichis in communication with said first gas introducing section.
 9. Asubstrate processing apparatus as recited in claim 8, wherein said gasheating tube further includes a sixth tube disposed in said seconddirection along said first plate, said gas introducing tube being incommunication with said one end of each of said first and third tubesthrough said sixth tube.
 10. A substrate processing apparatus as recitedin claim 3, wherein said gas heating tube extends from said first gasintroducing section side toward said gas exhausting section side, isbent back before an end of said substrate at said gas exhausting sectionside, and extends from said gas exhausting section side toward saidfirst gas introducing section side.
 11. A substrate processing apparatusas recited in claim 10, wherein said gas heating tube extends from saidfirst gas introducing section side toward said gas exhausting sectionside, is bent back before the central portion of said substrate orbefore the vicinity of the central portion of said substrate, andextends from said gas exhausting section side toward said first gasintroducing section side.
 12. A substrate processing apparatus asrecited in claim 10, whereinsaid gas heating tube is disposed along bothof said fourth and fifth plates.
 13. A substrate processing apparatus asrecited in claim 3, whereinsaid gas discharging section of said gasheating tube is provided along said first plate, and said gasdischarging section includes a plurality of gas discharging holesprovided substantially parallel to said second direction.
 14. Asubstrate processing apparatus as recited in claim 13, whereinsaidreaction tube body is substantially symmetrical in said second directionwith respect to a line in said first direction, said substrate holder issubstantially symmetrical in said second direction with respect to saidline, and being capable of holding said substrate substantiallysymmetrically in said second direction with respect to said line, saidgas heating tube is substantially symmetrical in said second directionwith respect to said line, and said plurality of gas discharging holesare disposed substantially symmetrically in said second direction withrespect to said line.
 15. A substrate processing apparatus as recited inclaim 13, wherein said plurality of gas discharging holes are arrangedfrom the vicinity of a first corner portion formed between said firstand fourth plates to the vicinity of a second corner portion formedbetween said first and fifth plates.
 16. A substrate processingapparatus as recited in claim 13, wherein said first gas introducingsection of said reaction tube body includes an opening provided in saidfirst plate, said opening exposing said plurality of gas dischargingholes.
 17. A substrate processing apparatus as recited in claim 3,whereinsaid first gas introducing section includes a plurality of gasintroducing holes provided in said first plate, substantially parallelto said second direction.
 18. A substrate processing apparatus asrecited in claim 17, whereinsaid reaction tube body is substantiallysymmetrical in said second direction with respect to a line in saidfirst direction, said substrate holder is substantially symmetrical insaid second direction with respect to said line, and is capable ofholding said substrate substantially symmetrically in said seconddirection with respect to said line, said gas heating tube issubstantially symmetrical in said second direction with respect to saidline, and said plurality of gas introducing holes is substantiallysymmetrical in said second direction with respect to said line.
 19. Asubstrate processing apparatus as recited in claim 17, wherein saidplurality of gas introducing holes are arranged from the vicinity of afirst comer portion formed between said first and fourth plates to thevicinity of a second corner portion formed between said first and fifthplates.
 20. A substrate processing apparatus as recited in claim 1,whereinsaid first gas introducing section and said gas exhaustingsection are separated in a first direction, said reaction tube body issubstantially formed in a rectangular parallelepiped shape, saidreaction tube body includes a first plate substantially perpendicular tosaid first direction, a second plate and a third plate substantiallyparallel to a first plane which includes said first direction and asecond direction perpendicular to said first direction, and fourth andfifth plates which are substantially parallel to said first directionand are substantially perpendicular to said first plane, and a sixthplate disposed, substantially perpendicularly to said first direction,at the opposite side of said first plate, said first gas introducingsection is provided in said first plate, and said sixth plate isprovided with said gas exhausting section.
 21. A substrate processingapparatus as recited in claim 1, wherein said gas heating tube issecured to said reaction tube body.
 22. A substrate processing apparatusas recited in claim 1, wherein said substrate processing apparatus is ofa hot-wall type.
 23. A substrate processing apparatus as recited inclaim 1, wherein said reaction tube body has a structure such that asubstrate, or a small number of substrates are held.
 24. A substrateprocessing apparatus as recited in claim 1, wherein said substrate is asemiconductor wafer.
 25. A hot-wall type substrate processing apparatus,comprising:a reaction tube body including a first gas introducingsection and a gas exhausting section separated by a distance from eachother in a first direction, a first plate substantially perpendicular tosaid first direction and having said first gas introducing section, asecond plate and a third plate substantially parallel to a first planeincluding said first direction and a second direction substantiallyperpendicular to said first direction; and fourth and fifth plates whichare substantially parallel to said first direction and are substantiallyperpendicular to said first plane; a heater facing one or both of saidsecond and third plates; a substrate holder disposed in said reactiontube body and being capable of holding a substrate within said reactiontube body between said first gas introducing section and said gasexhausting section in a state where a face of said substrate to beprocessed is substantially parallel to said first plane; and a gasheating tube provided along one or both of said fourth plate and saidfifth plate, and having a second gas introducing section and a gasdischarging section which is in communication with said first gasintroducing section.
 26. A substrate processing apparatus as recited inclaim 25, wherein said gas heating tube is also disposed along saidfirst plate.
 27. A substrate processing apparatus as recited in claim25, wherein said heater is provided such as to face said second plateand said third plate.